An ethylene-vinyl alcohol copolymer, which henceforth may be abbreviated as EVOH, is superior in transparency and gas barrier property, but it has defect of being poor in stretchability, flexibility and flexing resistance. Known is a method of blending a flexible resin such as an ethylene-vinyl acetate copolymer and an ethylene-propylene copolymer to an EVOH to improve the defect. However, this method has a defect that transparency deteriorates greatly.
In addition, known is a melt-molding material which is superior in stress cracking resistance, polar solvent resistance and water resistance and has both good barrier properties to gas such as oxygen and superior moldabilities, especially stretchability, which comprises a silicon-containing EVOH having an ethylene content of 25-60 mol %, a degree of saponification of 95 mol % or more and a silicon content of 0.0005-0.2 mol % (see JP-A-60-144304).
JP-A-50-12186 discloses a method for producing a modified EVOH with an improved mold-workability, the method being characterized by reacting 0.01-0.8 parts by weight of polyfunctional epoxy compound with 100 parts by weight of EVOH having an ethylene content of 20-90 mol % and a degree of saponification of 95% or more.
However, in the conventional technology mentioned above, none of the stretchability, flexibility and flexing resistance which EVOH has is necessarily sufficient. Furthermore, the stretchability, flexibility and flexing resistance of EVOH and the transparency of EVOH are not satisfied at the same time.
In JP-A-50-12186, an improvement in neck-in (a phenomenon that a product width becomes narrower than die slit width) which occurs when an EVOH is shaped into a film through a T-die is disclosed as an improvement in mold-workability. However, there is no description about the improvement in stretchability, flexibility and flexing resistance, which is the object of the present invention. In addition, no effects of improving in stretchability, flexibility and flexing resistance are not obtained with the EVOH described in the above-cited publication, which was reacted with a specific amount of polyfunctional epoxy compound. Furthermore, in the case of using a polyfunctional epoxy compound, it is difficult to produce an EVOH whose amount of modification with an epoxy compound is within the specific range specified in the present invention.
An object of the present invention is to provide a modified ethylene-vinyl alcohol copolymer which is superior in barrier property, transparency, stretchability, flexibility and flexing resistance and a barrier material comprising the same. In addition, the invention provides a method for producting such a modified ethylene-vinyl alcohol copolymer.